Idun already knew that another deity was in the crowd. She wasn't bothered by the silent acknowledgment in her mind because she already knew about the source. That was a fun bonus when she happened to be kind of stalking a goddess from another pantheon. Idun wasn't startled by her presence. But even the slightest hint of that would be detrimental to her entire mission, so Idun decided her plan needed a sub-plan. A mini plan, perhaps. If she was going to pull off this random meeting, she needed to act truly surprised as the goddess got closer and closer and, eventually, came into view. Idun didn't turn her head at first, but she could feel it, feel the proximity knocking on the door at the back of her mind, demanding some sort of acknowledgment.
Idun turned quickly, once she hammered out the details of her sub-plan. She glanced in Melinoe's general direction, then turned to face forward again. A moment later, she turned again, brow slightly furrowed, and this time her gaze found that of the other goddess. Realization seemed to wash over her. It was all very, very convincing. And why shouldn't it be? Idun was married to the god who brought some of the best plays ever written to the stage. She spent a good amount of time around actors, and some of those actors not only needed to convey emotion convincingly, but they also needed to do so while somewhat-convincingly playing the part of a woman.
And if that didn't count as experience, the entire first stage of her relationship with Bragi left her playing the part of someone who was absolutely, one hundred-percent not madly in love. Idun was so convincing, she even had herself fooled.
Looking surprised was a walk in the park compared to that.
She smiled once the shock was allowed to sink in a bit, and then she decided to approach. Melinoe clearly wasn't going to. Maybe she was shy. Idun couldn't say for sure yet, but she'd find out. A dozen or so 'Excuse mes' later, Idun made it to the other goddess, and the smiling just kept on happening.
"Hi! I'm Idun. Norse. I didn't realize anybody else was a Cyndi fan. What are the odds, right? And you're Greek, right? That's so great!" she half-shouted. Talking at a concert was never an easy task, but she'd manage. Shouting was really just talking with extra enthusiasm, after all.